The present invention is in the area of tape cassettes for video and audio tape players and recorders, and pertains more specifically to spools used in said cassettes which are specifically designed to perform or aid in the performance of testing functions in the manufacture or service of such tape players and recorders.
In this specification the term tape recorders will be used to mean playing and recording machines for all kinds of recording type, regardless whether such a machine is limited to playing or recording, or whether it may do both.
In many kinds of tape recorders it is common for the tape to be supplied to the recorder in a cassette, the cassette having a supply reel and a take-up reel. In loading, the cassette is supplied to the tape recorder, and the recorder typically has a mechanism for accepting the cassette and positioning it relative to the drive mechanisms and the playing or the recording head. In operation, whether recording or playing, the take-up reel is typically driven and tape is supplied at a constant rate from the supply reel. Due to the thin and typically fragile nature of the recording tape, it is typical for tape recorders to have a tape tensioning mechanism to maintain a relatively consistent or constant tape tension during transition from a fully supply reel to an empty supply reel.
In operation, while recording or playing, the take-up reel is typically driven, pulling the tape exiting from the capstan as it is pulled from the supply reel. A tape tensioning mechanism typically acts by supplying a torque to the supply reel opposite the direction of rotation of the supply reel.
FIG. 1 shows a reel 11 acting as the supply reel of a cassette and tape 13 wound on the reel with the tape being pulled off the reel in the direction of arrow 15. A torque of magnitude Q is applied by a tensioning mechanism to shaft 17, and the resulting torque is in the rotary direction of arrow 19.
Assuming a tape of relatively constant width and thickness, the tension T in the tape can be represented by the total pull force on the tape in the direction of arrow 15. In this case the tension will be represented by force terms, such as grams, rather than by force per unit area. If the tensioning mechanism maintains a constant torque Q on shaft 17, then the torque will be substantially balanced by the tension T multiplied by the radius R1. That is: T.times.R1=Q. As an example, under these circumstances, if the torque Q applied to shaft 17 is 90 gram-cm. and the radius R1 is 3.0 cm., the tape tension T, as a force, will be 30 grams.
If the radius R1 is the radius of the reel and tape in the full condition, before playing or recording begins, the radius will gradually change during operation until substantially the end of the tape is reached, and the radius at that time will be the radius of an empty supply reel, R2. Assuming R2=1.0 cm., if the torque Q does not change, and is maintained through operation at essentially 90 gram-cm., as in the first example, the tape tension T (force) will be, when the reel is substantially empty, T=90 grams. This is three times the value at the beginning of operation. For this reason it is common for tape tensioning mechanisms to be servo-driven to vary the torque on the supply reel to keep the tape tension substantially constant.
It is important in quality control to be able to test the performance of tape tensioning mechanisms in tape recorders quickly and easily during manufacture and in service and maintenance procedures. To properly test the operation of a tape tensioning mechanism, readings must be taken both with a fully supply reel and with a substantially empty supply reel, and the readings should be taken at a tape speed substantially the same as the normal tape speed in operation. To do so presently is time consuming, because after a tension measurement is made with a full reel, nearly all the tape must be unwound from the reel to make a tension measurement with the reel nearly empty.
The present invention provides a cassette and a method for making the two necessary measurements at the two extremes of operation quickly and easily.